SO not a lawyer but the situation seems to be the fault of the other driver. Considering that there was a traffic incident up ahead (I'm assuming you could see the incident) it's not out of the realm of possibilities that he was well aware of the traffic situation. Given the gap space between you and the driver is 10 feet, and you had already crossed the lane line with your car, properly signaled, had he failed to apply the breaks it would have been because he was aggressively trying to intimidate another driver on the road. I haven't looked up the law, but California does have laws against aggressive driving and road rage, and the driver's behavior could be a violation of the law in and of itself, which greatly puts culpability on the driver if proven. If such an accident occurs, you should get his insurance information and then make sure to get contact information for any witnesses, especially if they can back you you up. If the driver is hostile, call 911 and let them know that you are in an accident and do not feel safe exiting your vehicle and why (the other driver) so there is a record of your statements in the moment. Avoid any statements that could be construed as guilt to the other drive (I am so sorry might be hostile, but a lawyer may use that to imply you knew you did something wrong) and don't be aggressive.
Tactically, in a lane closure I have found that the furthest lane from the accident is going to be the one that moves the quickest and that by waiting until the merge is forced by responding units. The closed lane will merge into the opened lanes in a zipper style (open lane car followed by one closed lane car followed by open lane car) and instructions given by police officers always supercede posted restrictions and rules of ordinary operation (If a cop waves you through a red light, you won't be penalized for driving without the right of way through an intersection.).
Again, ultimately who is at fault is up to the cops who respond and if no summons is given, your insurance company will pay out for you, the other driver's company pays for him, and then the companies deal with each other and the company who's client is at fault reimburses the non-fault driver's company and assess the driver for a higher payment based on their record. You only need to worry if the damage involved an injury to persons or damages in excess of your coverage, both of which don't seem possible based on the speed the other driver could reach before an impact.
Edit: As a general rule, in the United States if two cars are traveling in the same direction, and Car A is in front of Car B, The driver of Car A is usually not responsible for any accident with Car B nor if the force of the impact causes Car A to impact another car ahead of it. In your case, since your car had safely crossed into the other lane and the driver was behind you and still proceed in a manner that would have caused an accident, he would likely be at fault. The more over the line the better, but since you were already in the merging process far enough that he could not overtake you at his present speed, he was effectively the Car B.